Generally, facial state values of an object person indicating a facial direction, a state of blinking and a line of sight are estimated by use of facial feature values of a mouth, a nose and the like extracted from a face image of the object person. In a case where the object person is wearing a mask and/or sunglasses, however, those facial state values may not be accurately estimated. A patent document JP2003-296712A discloses a method for estimating a direction of a face of an object in consideration of a covering, such as a mask and/or sunglasses, attached to the face. According to the known method, an operational circuit extracts feature points of eyes, a mouth and a nose from a face image and, on the basis of the extracted feature points, the face direction is estimated. In this method, when the feature points indicating eyes are not extracted for a repetitive number of times, the operational circuit determines that the object is wearing sunglasses, and the face direction of the object is estimated by use of image features on the sunglasses. Further, when the feature points indicating that the nose and the mouth are not extracted for a repetitive number of times, the operational circuit determines that the object is wearing a mask, and the face direction of the object is estimated by use of image features on the mask.
According to the known method, the operational circuit determines that the object is wearing the mask and/or the sunglasses when the feature values corresponding to the eyes, the nose and the mouth are not extracted, however, in a case where a face direction of a driver driving a vehicle is estimated, feature points of the eyes, nose and mouth may not be detected frequently, even when the driver is not wearing a mask and/or sunglasses. Specifically, such misdetection may occur due to a change of a local brightness in the face image caused by variations of luminosity in an actual driving environment, a posture of the driver's face and the like. Accordingly, even when the driver is not wearing the sunglasses and/or the mask, because the operational circuit may determine that the driver is wearing the sunglasses and/or the mask due to the misdetection described above, a facial state value indicating the direction of the driver's face may be estimated on the basis of the feature point on the sunglasses and/or mask that do not actually exist. As a result, an accurate facial state value is not obtained, and further a facial state value having a large error may be calculated.
A need thus exists for an object determining device and a program thereof which are not susceptible to the drawback mentioned above.